Dog making weird noises

Hi, my 1.5 year old dog will randomly make noises that sound like he is trying to clear his throat. It's not coughing. It's definitely not kennel cough because it's been going on for awhile. He will breathe in and out for about 3 seconds while making the noise like clearing his throat. We tried asking the vet but they said it's hard to know but they didn't seem concerned. This happens probably a couple times a week. Does anyone have any ideas what this is or why he is doing it?